You should not rely on your opponent wasting time like the way black did. Can you show me established players playing like that? (Other than the King Gambit/Fried Liver Attack days.)
It's actually a dangerous opening. Plenty of Strong GM's have played the Grand Prix Attack, although Black has found remedies to his problems with a ..g6 ..Bg7 set up. ..h6 and ..Bd7 both seem like mistakes, or at least inaccuracies. For sure ..h6. At least Bd7 develops a piece.
Tiviakov didn't play the main idea of this line in that game, though, which is to flick in an early f5 and go straight for a mate on the kingside. Shame - I would like to have seen Kasparov refute that (I'm sure he would) - it would be useful for my OTB and blitz games! Interesting that Kasparov himself plays ...f5, something you also sometimes see black play against the kingside expansions for white in the Closed Sicilian proper.